The so-called BMA process (hydrocyanic acid-methane-ammonia process) for the production of hydrogen cyanide or hydrocyanic acid starts out from methane and ammonia and operates in the absence of oxygen or air.
According to German patent application No. P2913925.1-41 and related Voigt U.S. application Ser. No. 133,358 filed Mar. 24, 1980, it has already been proposed to employ liquified gas, e.g. propane, n-butane, i-butane or mixtures of two or more of them, in place of methane. The entire disclosure of Voigt is hereby incorporated by reference and relied upon.
The reaction itself is carried out in suspended reaction tubes made of sintered aluminum oxide which are internally coated with a platinum catalyst.
Since the reaction proceeds endothermally, the reaction tubes are heated and thereby there are obtained reaction temperatures of around 1300.degree. C. In order to avoid the occurrence of reverse reaction the hydrogen cyanide containing gas mixture formed must be cooled off quickly to a temperature below 400.degree. to 300.degree. C. this takes place in a water cooled chamber made of aluminum in the top of the furnace itself, see Ullmann, Enzyklopadie der technischen Chemie, 4th edition, Vol. 9, pages 659-660; Dechema-Monografie, 1959, No. 33, pages 28-46 and also German Pat. No. 959,364.
In carrying out the so-called BMA process it has been shown that a certain part of the ammonia employed in the reactor is lost with the gaseous product.
This non-reacted part of ammonia is lost for the production of hydrogen cyanide since the ammonia in customarily was washed out of the gaseous product with sulfuric acid and a working up of the ammonia sulfate thus recovered in order to recover the ammonia therefrom was much too expensive industrially and therefore uninteresting.
The other known processes for removal of ammonia from gaseous mixtures, as e.g. with aqueous solutions, acid acting absorption agents such as acid salts of phosphoric acid or lower fatty acids or the removal of ammonia with specific boric acid complexes, with solutions of ammonium nitrate or with urea as well as with specific heavy metals salts also cannot solve all of the problems of an easy recovery of the ammonia, see German Pat. No. 1191347.
Of course it is known that adsorption methods for the removal of ammonia from gaseous streams also are suited but with longer sorption of hydrogen cyanide containing gases there is a partially polymerization or decomposition of the hydrogen cyanide in the gas stream. Therefore customary sorption agents such as activated carbons or silica gel cannot be used, see Gmelin, Vol. 14 C [D 1], pages 218-220, particularly page 219 and R. F. Barrow et al in J. Chem. Soc., 1947, pages 401-416.
Thus it appeared that the residual ammonia leaving with the gaseous product was lost for the BMA process itself.
This situation was most unsatisfactory.
The object of the invention is to develop an industrially simple process for the recovery of ammonia within the so-called BMA process in which the so recovered ammonia can again be returned into the reactor.